1. Field of the Invention
This invention relates to a new aid for the stimulation of plant growth. More specifically it pertains to the use of caulerpin as a growth promoter for various plants.
2. Description of the Prior Art
Caulerpin is a red crystalline substance derived from certain species of the marine alga Caulerpa and was first reported by Aguilar-Santos and Doty in a symposium on Aug. 27-29, 1967 at the University of Rhode Island. It is identified as dimethyl 5,12-dihydrocyclooctal (1,2-b : 5,6-b') di-indole-6,13-dicarboxylate as was first determined by Maiti, Thomson and Mahendran and reported in the Journal of Chemical Research, 1978.
Various physical evidence attributes the formula to be: ##STR1##
This is considered to be a dimer of indole-3-acrylic acid which has the formula: ##STR2##
Careful search of the literature has found no suggestion of any activity of Caulerpin as a plant growth regulator or hormone.
Various methods of extracting Caulerpin from the powdered or whole alga Caulerpa have been described in the following publications: Aguilar-Santos, J. Chem. Soc. (C) 1970, pp. 842-3; the University of Rhode Island Symposium on "Drugs From The Sea", Aug. 22-29, 1967, (Ed. H. Freudenthal, Publ. of the Marine Technological Society, J. of Ocean Techn., (1968); Maiti, Thomson and Mahendran, J. Chem. Res. (s) pp. 126-7 and (m) pp. 1683-93 (1978); McConnell, Huges Targett, and Daley, J. Chem. Ecol. 8, 1437-51; Vest, Dawes and Romeo, Botanica Marina 26, 313-6 (1983); and Santos and Doty, Lloydia 34, 88-90 (1971). The test compound used hereinafter is derived by the method described in the above listed McConnell et al reference.
Among the indolic auxins, strong auxin activity has long been known to be associated with even number of carbon atoms in the side chain, e.g., indole-3-acetic acid, and indole-3-butyric acid and 2 and 4 C atoms respectively, while C3 side chains such as indole-3-propionic and indole-pyruvic acids show weaker activity in most tests (Thimann, K. V., 1972, Physiology of Development, The Hormones, in Plant Physiology Ed. F. C. Steward, Vol. VIB, Academic Press, New York). Unsaturation in the side chain is further associated with weakening of auxin effects. With regard to caulerpin the side chains which might carry chemical activity are cross-bonded to the indole nucleus reciprocally, such that they would be presumed inactive.
It is generally believed that the activity of natural auxins in plant growth is accompanied by production of ethylene, which has many physiological effects related to ripening of fruit, senescence, stress and wound responses, and to inhibition of root growth. Interaction of auxins and ethylene with other plant hormones is thought to achieve balance under normal conditions at various stages of growth and reproduction. Indeed, a number of auxin bio-assays, such as the cress root test, are based upon the ability of auxins to limit root growth when applied in moderate to high concentrations.
Hofinger, Archives Internationales de Physiologie et de Biochimie, 77, 225-30 (1969), reported indole-3-acrylic acid to be present in peas, lentils, and lupines (all members of the pea family Fabaceae), where it was thought to function as the principal auxin. The question of extraction artefact has subsequently arisen. Test results on lentil root sections, however, showed inhibition of growth in concentrations ranging down to 5.times.10.sup.-7 M, with slight stimulation in the order of 2-8% below that level, with effects disappearing at 10.sup.-9 M. Hofinger, Gaspar, and Menard, (Comptes rendus, Acad. Sci. Paris, t. 290 (14 Ja., 1980) report stimulation of ethylene production in lentil roots in concentrations above 10.sup.-7 M. and inhibition below this level to 10.sup.-9, the limit of activity.
Shimokawa, Phytochemistry, 22 1903-8 (1983), working with an ethylene forming enzyme obtained from Citrus unshiu (Satsuma orange), found that indole-3-acrylic acid non-competitively inhibited ethylene formation from 1-aminocyclopropane-1-carboxylic acid. However, in vivo, these results were not always reproduced. Endogenous ethylene production by apple tissue in vivo was not inhibited.
With reference to the marine environment, Augier has presented an exhaustive and definitive review of the subject of growth-active substances of marine plants (Botanica marine, 7 fascicles, 1976-78). However, neither indole-3-acrylic acid nor caulerpin is mentioned. Codomier, Segot and Teste (Botanica marine, 22:153-7, 1979) studied the effect of various phytohormones on the growth of Asparagopsis armata (marine alga, Rhodophyta). At 10.sup.-4 M, indole-3-acrylic acid inhibited the growth of the crozier-like hooks of this species, but showed limited stimulation initially at 10.sup.-5 and 10.sup.-7 M.
In certain cases potent auxins can overstimulate growth to the point of causing defoliation, or a herbicidal effect, or a stunting effect. For example, indole-3-acetic acid, beta-naphthoxyacetic acid and 2,4-dichlorophenoxyacetic acid can produce such effects.